DESCRIPTION: This is the first continuation of an imaginative program of research aimed at using trapping methods to isolate reaction intermediates, and then study their structures using either monochromatic X-rays or Laue crystallography, as appropriate. The first project period led to a number of successful experiments, both in terms of method development and also in terms of actual intermediates that were studied. Building on this valuable experience, Dr. Stoddard now proposes to move in three directions: (i) to determine the structure of a cleaved hammerhead ribozyme structure, (ii) to see if the ribozyme cleavage reaction can be studied in time (iii) to determine the structures of two members of a novel class of endo nucleases, the intron coded enzymes CreI and PpoI. After structure determination by MIR, these enzymes will then be utilized in studies aimed at determining the structures of reaction intermediates. (iv) Dr. Stoddard aims to develop solvent trapping methods to study chemically labile intermediates. Specifically, he plans to study the reaction of the Michaelis complex of the superoxide anion and superoxide dismutase.